This invention relates to the data acquisition components of spectrometer systems, and deals particularly with the computer interface system needed if a plurality of spectral scanning units are to be combined in a single spectrometer system, and if the spectral scanning units need to be located at substantial distances from one another and/or from the main control computer(s).
In a spectrometer system, a single computer unit has traditionally been used to provide both data-acquisition control and data-manipulation. This is accomplished by combining, in effect, two processors in one box. These processors, often referred to as "A" and "B" processors, are provided with a high speed parallel interface. The "B" processor controls data acquisition at the interferometer; and the "A" processor controls processing (including Fourier transform) of the data received from the interferometer.
Although the present invention is useful in any complex spectrometer systems, including laboratory systems, its development was motivated primarily by the problems of process monitoring situations, and of harsh duty quality control situations.
The user needs most often voiced in these situations are: reliability, ruggedness, vibration tolerance, insensitivity to ambient temperature variations, acceptable cost, and the ability to operate the optics remotely from the computer hardware. If feasible, major benefits would be provided by systems which permit using multiple, remotely located optical heads [remote from the central processing unit (CPU), and remote from one another]. Such optical heads may be located in crowded or hazardous environments, with the CPU in a remote and benign atmosphere, e.g., a control room. In some situations, it is desirable to permit separation of an optical head from a CPU by a distance as long as 3,000 ft.
In an effort to solve the problems encountered in process monitoring environments, the separation of the A and B data processors was tried by the assignee of the present application. A data acquisition control processor was included in each of a plurality of separate optical heads remotely located at various process observation points. One or more CPU computers were used to interface with the remote optical heads. Providing efficient intercommunication of the remote optical heads with the CPU(s) became a significant problem.
In approaching this problem, applicant's first effort was to extend the length of the existing parallel linking system sufficiently to provide the desired remote control. This would have avoided the complications involved in translating information from parallel to serial, and then back to parallel again. The data rates with such serial connections were considered too low, and the costs too high.
However, after a period of experimentation, it was determined that the parallel linking plan had many problems, including reliability problems, time of flight delays from the CPU out to the end of the line and back, and problems in making a multiple drop (where one CPU could communicate simultaneously with more than one optical head).
Another roadblock encountered was the standard approach to CPU control of multiple local computers, which involved transmitting back and forth signals from the CPU to each local computer on a separate line (a "spokes in the wheel" architecture). This type of system is not efficient because of the very long aggregate signal travel distances involved.